package udp

import (
	"context"
	"fmt"
	"net"
	"strings"
	"sync"
	"syscall"
	"time"

	"golang.org/x/net/ipv4"

	"hamlog/internal/applog"
)

// reusingListenConfig builds a net.ListenConfig that sets SO_REUSEADDR
// (and SO_REUSEPORT on Unix) on the underlying socket before bind. This
// is the only way for two processes to share a UDP port on Windows — Go
// doesn't expose the option directly, but ListenConfig.Control hooks the
// raw socket and lets us call setsockopt.
func reusingListenConfig() net.ListenConfig {
	return net.ListenConfig{
		Control: func(network, address string, c syscall.RawConn) error {
			var opErr error
			err := c.Control(func(fd uintptr) {
				opErr = setSocketReuse(fd)
			})
			if err != nil {
				return err
			}
			return opErr
		},
	}
}

// Event is what a Server emits to its consumer for every parsed packet.
// At most one of the fields is populated per event.
type Event struct {
	ConfigID  int64
	Service   ServiceType
	Source    string // remote addr that sent the packet, for diagnostics

	DXCall     string     // ServiceWSJT (Status) or ServiceRemoteCall
	DXGrid     string     // ServiceWSJT (Status)
	Mode       string     // ServiceWSJT (Status)
	FreqHz     int64      // ServiceWSJT (Status)
	LoggedADIF string     // ServiceWSJT (LoggedADIF), ServiceADIF or ServiceN1MM
}

// Server is a single inbound UDP listener.
type Server struct {
	cfg     Config
	conn    *net.UDPConn
	out     chan<- Event
	stop    chan struct{}
	done    chan struct{}
	stopped bool
	mu      sync.Mutex
}

func newServer(cfg Config, out chan<- Event) *Server {
	return &Server{
		cfg:  cfg,
		out:  out,
		stop: make(chan struct{}),
		done: make(chan struct{}),
	}
}

func (s *Server) start() error {
	var conn *net.UDPConn
	if s.cfg.Multicast {
		group := strings.TrimSpace(s.cfg.MulticastGroup)
		if group == "" {
			return fmt.Errorf("multicast enabled but group address is empty")
		}
		groupIP := net.ParseIP(group)
		if groupIP == nil {
			return fmt.Errorf("bad multicast group %q", group)
		}
		gaddr := &net.UDPAddr{IP: groupIP, Port: s.cfg.Port}
		// Bind to INADDR_ANY:port so the kernel will forward packets
		// addressed to the multicast group from any interface. Then
		// JoinGroup() on every up & multicast-capable interface — Windows
		// won't route multicast through interfaces we haven't explicitly
		// joined, and the "default" interface picked by
		// net.ListenMulticastUDP isn't always the one MSHV/WSJT sends on.
		// ListenConfig with SO_REUSEADDR lets us share the port with
		// Log4OM / other listeners already bound to 2237.
		lc := reusingListenConfig()
		pc, err := lc.ListenPacket(context.Background(), "udp4", fmt.Sprintf("0.0.0.0:%d", s.cfg.Port))
		if err != nil {
			return fmt.Errorf("listen :%d for multicast: %w", s.cfg.Port, err)
		}
		c, ok := pc.(*net.UDPConn)
		if !ok {
			_ = pc.Close()
			return fmt.Errorf("internal: ListenPacket returned %T not *net.UDPConn", pc)
		}
		p := ipv4.NewPacketConn(c)
		ifaces, _ := net.Interfaces()
		joined := 0
		for _, ifi := range ifaces {
			if ifi.Flags&net.FlagUp == 0 || ifi.Flags&net.FlagMulticast == 0 {
				continue
			}
			if err := p.JoinGroup(&ifi, gaddr); err != nil {
				applog.Printf("udp: [%s] join %s on %s: %v\n", s.cfg.Name, gaddr.IP, ifi.Name, err)
				continue
			}
			joined++
		}
		if joined == 0 {
			_ = c.Close()
			return fmt.Errorf("couldn't join multicast %s on any interface", gaddr.IP)
		}
		conn = c
		applog.Printf("udp: [%s] listening on multicast %s on %d interface(s) (service=%s)\n",
			s.cfg.Name, gaddr, joined, s.cfg.ServiceType)
	} else {
		lc := reusingListenConfig()
		pc, err := lc.ListenPacket(context.Background(), "udp4", fmt.Sprintf("0.0.0.0:%d", s.cfg.Port))
		if err != nil {
			return fmt.Errorf("listen udp :%d: %w", s.cfg.Port, err)
		}
		c, ok := pc.(*net.UDPConn)
		if !ok {
			_ = pc.Close()
			return fmt.Errorf("internal: ListenPacket returned %T not *net.UDPConn", pc)
		}
		conn = c
		applog.Printf("udp: [%s] listening on unicast :%d (service=%s)\n", s.cfg.Name, s.cfg.Port, s.cfg.ServiceType)
	}
	s.conn = conn
	go s.run()
	return nil
}

func (s *Server) run() {
	defer close(s.done)
	buf := make([]byte, 64*1024)
	for {
		select {
		case <-s.stop:
			return
		default:
		}
		_ = s.conn.SetReadDeadline(time.Now().Add(500 * time.Millisecond))
		n, remote, err := s.conn.ReadFromUDP(buf)
		if err != nil {
			if ne, ok := err.(net.Error); ok && ne.Timeout() {
				continue
			}
			// Closed by stop(): exit silently.
			return
		}
		if n == 0 {
			continue
		}
		pkt := make([]byte, n)
		copy(pkt, buf[:n])
		go s.handle(pkt, remote)
	}
}

func (s *Server) handle(pkt []byte, remote *net.UDPAddr) {
	applog.Printf("udp: [%s] rx %d bytes from %s\n", s.cfg.Name, len(pkt), remote)
	ev := Event{ConfigID: s.cfg.ID, Service: s.cfg.ServiceType, Source: remote.String()}
	switch s.cfg.ServiceType {
	case ServiceWSJT:
		w, ok, err := ParseWSJT(pkt)
		if err != nil {
			applog.Printf("udp: [%s] WSJT parse error: %v\n", s.cfg.Name, err)
			return
		}
		if !ok {
			applog.Printf("udp: [%s] WSJT msg type ignored\n", s.cfg.Name)
			return
		}
		applog.Printf("udp: [%s] WSJT decoded: prog=%q dx_call=%q grid=%q mode=%q freq=%d adif_len=%d\n",
			s.cfg.Name, w.ProgramID, w.DXCall, w.DXGrid, w.Mode, w.FreqHz, len(w.LoggedADIF))
		ev.DXCall = w.DXCall
		ev.DXGrid = w.DXGrid
		ev.Mode = w.Mode
		ev.FreqHz = w.FreqHz
		ev.LoggedADIF = w.LoggedADIF
	case ServiceADIF:
		// JTAlert / GridTracker forward a text ADIF record after a QSO is
		// logged. Guard against keep-alive / non-ADIF chatter on the socket:
		// only forward payloads that actually carry a callsign field and a
		// record terminator.
		text := string(pkt)
		low := strings.ToLower(text)
		if !strings.Contains(low, "<call:") || !strings.Contains(low, "<eor") {
			applog.Printf("udp: [%s] ADIF payload ignored (no <call:>/<eor>)\n", s.cfg.Name)
			return
		}
		ev.LoggedADIF = text
	case ServiceRemoteCall:
		// Common payload shapes seen in the wild:
		//   "F4XYZ"                       (bare callsign)
		//   "CALL F4XYZ"                  (text prefix)
		//   "<CALLSIGN>F4XYZ<CALLSIGN>"   (DXHunter-style tags)
		//   "<CALLSIGN>F4XYZ</CALLSIGN>"  (proper XML)
		// Strip every angle-bracket tag, normalise whitespace, take the
		// last non-empty token. Upper-case for downstream consistency.
		text := string(pkt)
		// Drop every <...> tag (open or close) — works for both
		// <CALLSIGN>...<CALLSIGN> and <CALLSIGN>...</CALLSIGN>.
		for {
			start := strings.IndexByte(text, '<')
			if start < 0 {
				break
			}
			end := strings.IndexByte(text[start:], '>')
			if end < 0 {
				break
			}
			text = text[:start] + " " + text[start+end+1:]
		}
		text = strings.TrimSpace(text)
		parts := strings.Fields(text)
		if len(parts) == 0 {
			return
		}
		ev.DXCall = strings.ToUpper(parts[len(parts)-1])
	case ServiceN1MM:
		adifText, ok, err := ParseN1MM(pkt)
		if err != nil {
			applog.Printf("udp: [%s] N1MM parse error: %v\n", s.cfg.Name, err)
			return
		}
		if !ok {
			applog.Printf("udp: [%s] N1MM datagram ignored (not a loggable contact)\n", s.cfg.Name)
			return
		}
		applog.Printf("udp: [%s] N1MM contact decoded (%d bytes ADIF)\n", s.cfg.Name, len(adifText))
		ev.LoggedADIF = adifText
	default:
		return
	}
	// Empty events are useless; skip.
	if ev.DXCall == "" && ev.LoggedADIF == "" {
		return
	}
	select {
	case s.out <- ev:
	default:
		// Drop on backpressure rather than block the read loop.
	}
}

func (s *Server) close() {
	s.mu.Lock()
	if s.stopped {
		s.mu.Unlock()
		return
	}
	s.stopped = true
	stop, done, conn := s.stop, s.done, s.conn
	s.mu.Unlock()
	if conn != nil {
		_ = conn.Close()
	}
	if stop != nil {
		close(stop)
	}
	if done != nil {
		<-done
	}
}

// ── Outbound emitter ──────────────────────────────────────────────────

// SendUDP sends payload to dst (host:port). Unicast or directed broadcast.
// Returns the error from the write; the connection is closed before return.
func SendUDP(dst string, payload []byte) error {
	conn, err := net.Dial("udp4", dst)
	if err != nil {
		return fmt.Errorf("dial %s: %w", dst, err)
	}
	defer conn.Close()
	_ = conn.SetWriteDeadline(time.Now().Add(2 * time.Second))
	_, err = conn.Write(payload)
	return err
}

// ── Manager ───────────────────────────────────────────────────────────

// Manager owns every inbound Server and exposes a helper to emit on
// outbound connections at QSO-save time. It reloads from the Repo on
// demand (after a CRUD change in the Settings panel).
type Manager struct {
	repo *Repo
	out  chan Event

	mu       sync.Mutex
	inbound  map[int64]*Server
	outbound []Config
}

func NewManager(repo *Repo) *Manager {
	return &Manager{
		repo:    repo,
		out:     make(chan Event, 64),
		inbound: map[int64]*Server{},
	}
}

// Events returns the channel inbound parsed events are delivered on.
// The app exposes these as Wails events.
func (m *Manager) Events() <-chan Event { return m.out }

// Reload restarts every server based on the current Repo contents.
// Existing servers are stopped, the snapshot is rebuilt from scratch.
// Errors on individual rows are logged via the returned slice; the
// caller can surface them in the UI.
func (m *Manager) Reload(ctx context.Context) []string {
	applog.Printf("udp: Reload() called")
	m.mu.Lock()
	old := m.inbound
	m.inbound = map[int64]*Server{}
	m.outbound = nil
	m.mu.Unlock()

	for _, s := range old {
		s.close()
	}

	cfgs, err := m.repo.List(ctx)
	if err != nil {
		applog.Printf("udp: Reload list failed: %v", err)
		return []string{fmt.Sprintf("load udp configs: %v", err)}
	}
	applog.Printf("udp: Reload found %d config(s) in DB", len(cfgs))
	var errs []string
	for _, c := range cfgs {
		applog.Printf("udp: cfg id=%d name=%q dir=%s service=%s port=%d mcast=%v group=%q enabled=%v",
			c.ID, c.Name, c.Direction, c.ServiceType, c.Port, c.Multicast, c.MulticastGroup, c.Enabled)
		if !c.Enabled {
			continue
		}
		if c.Direction == Outbound {
			m.mu.Lock()
			m.outbound = append(m.outbound, c)
			m.mu.Unlock()
			continue
		}
		srv := newServer(c, m.out)
		if err := srv.start(); err != nil {
			applog.Printf("udp: start %q failed: %v", c.Name, err)
			errs = append(errs, fmt.Sprintf("%s: %v", c.Name, err))
			continue
		}
		m.mu.Lock()
		m.inbound[c.ID] = srv
		m.mu.Unlock()
	}
	applog.Printf("udp: Reload done — %d server(s) running, %d error(s)", len(m.inbound), len(errs))
	return errs
}

// Outbound returns the active outbound configs matching a service type.
// Used by the QSO save path to push notifications to listeners.
func (m *Manager) Outbound(service ServiceType) []Config {
	m.mu.Lock()
	defer m.mu.Unlock()
	var out []Config
	for _, c := range m.outbound {
		if c.ServiceType == service {
			out = append(out, c)
		}
	}
	return out
}

// StopAll closes every running server. Called at app shutdown.
func (m *Manager) StopAll() {
	m.mu.Lock()
	old := m.inbound
	m.inbound = map[int64]*Server{}
	m.outbound = nil
	m.mu.Unlock()
	for _, s := range old {
		s.close()
	}
}